A universal mathematical model of non-photochemical quenching to study short-term light memory in plants

The concept of plant memory triggers a quite controversial dispute on the definition, extent or even existence of such. Because plants are permanently exposed to rapidly changing environments it is evident that they had to evolve mechanisms enabling them to dynamically adapt to such fluctuations. Recognizing memory as a timed response to changes of external inputs through amplification and integration of multiple signals, here we study the short-term illumination memory in Arabidopsis thaliana by monitoring fluorescence emission dynamics. For this, we designed an experiment to systematically determine the extent of non-photochemical quenching (NPQ) after previous light exposure. We propose a simplified, mathematical model of photosynthesis that includes the key components required for NPQ activation. Due to its reduced complexity, our model is universally applicable to other species, which we demonstrate by adapting it to the shadow-tolerant plant Epipremnum aureum. We demonstrate that a basic mechanism of short-term light memory, which is based on two interacting components, can explain our experimental observations. The slow component, accumulation of zeaxanthin, accounts for the amount of memory remaining after relaxation in darkness, while the fast one, antennae protonation, increases quenching efficiency. With this combined theoretical and experimental approach we provide a unifying framework that helps to uncover general principles of key photoprotective mechanisms across species.